Floral Studies inOctomeriaR. BR. (Orchidaceae: Pleurothallidinae)

Abstract

Octomeriais a well‐represented basal genus in the subtribe Pleurothallidinae, the main myophile group of the Orchidaceae. The systematics of the genus is based in leaf shape and degree of connation of sepals. In this study, we analyse comparatively the flower micromorphology of 15 species through light microscopy, histochemical tests and scanning electron microscopy, including most of the infrageneric groups proposed for the genus. The epidermal structures of sepals and petals are very similar, with oblong or isodiametric cells, stomata and trichome‐like structures adaxially. The lip presents a uniseriate epidermis with ovate to irregular cells and mesophyll with homogeneous parenchyma and idioblasts with raphides. Calluses and grooves in the lip were shown to be secretory regions. Histochemical tests in fresh flowers were positive for starch in the sepals, petals and lip and positive for osmophores in the lip. Three types of waxes were observed; one of them is described for the first time. Our study shows that despite similarities in the perianth, floral micromorphology indicated differences in the lip and column surfaces. Thus, this approach can be an important source of phylogenetic information for the genus.